The invention relates to a process for the gasification of solid, finely ground carbon-containing fuels by the use of oxygen-containing gases in an entrained-flow process at elevated pressure and a temperature above the slag melting point, in which a syngas is generated and liquid slag is separated on the walls of the gasification reactor, cooling of the high temperatures of the syngas not being achieved exclusively by adding a cooled gaseous, vaporous or liquid foreign agent or by injecting water after the syngas has been generated but by additional or post-gasification of biological or renewable fuels in the syngas flow during the generation process. The addition of renewable fuels is implemented in syngas discharge direction on at least one downstream burner level of the reaction chamber, by which it is possible to utilize the enthalpy of the hot syngas partly for the gasification of a renewable fuel. The invention also relates to an apparatus for the endothermic gasification of solid renewable fuels on a second burner level inside the reaction chamber or in the quench chamber of a cooled reactor which is enclosed in a pressure vessel.
A potential syngas generation process is the gasification of solid, carbon-containing fuels with oxygen or with oxygen-enriched air. By reaction of the fuel with the gas, the fuel usually being introduced into the reaction chamber in finely ground condition, a syngas is produced which consists of carbon monoxide and hydrogen as main components. If water vapour is added to the oxygen-containing gas, a syngas is obtained which also contains hydrogen. The fuels are typically converted in a reaction according to the entrained-flow process in the reaction chamber, in which oxygen or an oxygen-enriched gas is mixed with finely ground fuel under pressure and injected in a dust flame into the reaction chamber by means of one or more burners. In a typical embodiment of the process the temperature of the syngas thus obtained ranges between 1200 and 1600° C.
To dissipate the high temperature of the syngas quickly and efficiently and to prevent the downstream process units from caking, the syngas, once obtained, is submitted to a so-called quench process. Here, the syngas is mixed with a gaseous, vaporous or liquid substance of lower temperature or cooled by injection of water so that it is caused to dissipate its high internal enthalpy quickly and efficiently after the generation. Used as fuels are coal, coke, biomass or petroleum coke. The fuels are typically converted into a finely dispersed form by grinding prior to the gasification reaction. A typical grain size of the fuels prior to the gasification reaction ranges between 0.05 and 0.5 mm. To achieve optimum efficiency of the entrained-flow gasification, the fuel can be injected with a twist into the entrained-flow flame, which is performed by tangentially provided injection nozzles or burners with direction into the entrained-flow cloud.
For the quench process a large amount of gaseous, vaporous or liquid cooling agent or water is supplied, which can frequently be recycled only partly into the gasification process. Furthermore, a major part of the heat enthalpy of the syngas gets lost, as it is frequently necessary to recycle the cooling agent to the process by condensation and re-vaporisation. This is energy-intensive and requires a lot of equipment. It would be favourable to provide a process which uses the high internal energy of the obtained syngas in a downstream process. It is therefore the aim to provide a process which utilizes the heat enthalpy of the hot syngas for a downstream process in the entrained-flow gasification process already.
The invention achieves the aim by a process which supplies a renewable raw material to the reaction chamber via at least another burner level arranged downstream of the first burner level and which extends, in direction of the gas flow, across the rear section of the overall height of the reactor, by which another gasification reaction of the renewable raw material takes place in the reaction chamber. This reaction is endothermic so that a major part of the enthalpy inherent in the syngas can be utilized chemically for the subsequent reaction. The gasification of renewable fuels gives a low-ash syngas since vegetable raw materials contain a significantly lower portion of ash-forming combustion materials. In this way the syngas thus obtained has a considerably lower content of solids. By the downstream gasification of the renewable raw materials, the temperature of the syngas, especially in the reaction chamber, can be used and controlled energetically for cooling the gas, which results in the saving of process energy. The burners can be designed as such or as burner guns.
According to the state of the art processes for the gasification of biofuels or renewable fuels in a mixture with carbon-containing fuels are known. EP 1027407 B1 describes a process for the generation of fuel gas, syngas and reduction gas from renewable and fossil fuels by combustion in a burner with gaseous oxygen or oxygen-containing gases. When entering the reaction chamber, the fuel is caused to rotate in order to convey the mineral components, which are liquid due to the reaction temperature, from the gasification reaction towards the reactor wall and thus separate them. The gasification agent is introduced into the gasification reactor through a central opening in the bottom of the combustion chamber and forms a plunging jet. The gasifier is also supplied with a carbon-containing fuel, the feed point for the carbon-containing fuel not being described in more detail.